1. Field of the Invention
The present invention relates to a method for treating a liquid effluent heavily loaded especially with nitrogen and phosphorus, and also a device for implementing this method.
2. Description of Related Art
Liquid effluents heavily loaded especially with nitrogen and phosphorus, whether of urban, agricultural or industrial origin, pose a serious problem especially in the field of the environment. All the developing controversy concerning the level of nitrate present in ground water must be borne in mind.
National and/or international legislations tend increasingly to prohibit any disposal of liquid effluents, in which the amount of nitrogenized material is greater than a threshold which is tending to fall as a result of action by various pressure groups. Likewise as regards phosphorus, legislation limits the quantities tolerated for materials which are to be spread as manure.
Furthermore, while a benefit from the above-mentioned liquid effluents is often obtained by spreading them as manure, the nauseating odor which results is a source of conflict with the surrounding neighborhood.
Amongst the liquid effluents heavily loaded especially with nitrogen and/or with phosphorus, primarily pig slurry should be mentioned, and also liquid sludge created by purification stations.
Indeed, a certain number of methods and/or devices have already been proposed for reducing the nuisance caused by the spreading of such liquid effluents, but none of these is entirely satisfactory, especially with respect to the regulations which are currently envisaged.
Thus, one of the aims of the present invention is to provide a method for treating a liquid effluent heavily loaded especially with nitrogen and with phosphorus, which allows the nitrogenized charge to be reduced at least to the legally acceptable threshold.
Another aim of the present invention is to provide a method of this nature which allows such liquid effluents to be deodorized.
An additional aim of the invention is to provide such a method which is simple to implement at low cost.
These aims, and also others which will later become apparent, are achieved by a method for treating a liquid effluent heavily loaded especially with nitrogen and with phosphorus according to the present invention, which includes the following stages:
a) the addition of a basic reagent to the liquid effluent to obtain a pH in the range from 8.5 to 13; and
b) entrainment of the basified liquid effluent derived from stage a) in a stream of air.
Advantageously, the basic reagent added during stage a) is unslaked or slaked lime in the form of powder, paste or liquid. This reagent may have a lime concentration (Ca(OH)2) up to 1000 g/liter of reagent.
Preferably, stage b) is repeated a certain number of times for the same basified effluent with the passage number typically being in the range from 1 to 50.
Advantageously, at the start of stage b) an anti-foam catalyst is added, the quantity of which varies from 0 to 1 liters per cubic meter of liquid effluent which is to be treated.
According to a preferred form of embodiment, the method in accordance with the present invention may comprise a third stage or stage c) of sifting of the liquid effluent derived from stage b).
As previously indicated, the present invention likewise concerns a device for implementing the above method, which is of low cost. This device comprises a mixing reactor for contacting the liquid effluent with the basic reagent, provided with an intake for this effluent and another intake for the basic reagent; an ammonia-extracting reactor, connected to the mixing reactor; and a tank for storing the treated liquid effluent derived from the ammonia-extracting reactor.
Advantageously, the mixing reactor comprises a device for measuring the pH of the medium connected to a means situated on the intake of basic reagent to automatically regulate the quantity thereof which is added.
Preferably, the ammonia-extracting reactor or degassing reactor comprises a lower part collecting especially the basified liquid effluent and an upper part in which is situated a diffusing rack provided with nozzles, connected to the lower part of the reactor which includes a feed pump. Openings are provided between the two parts so that the exterior air can enter, and an air exhaust fan is connected to the upper part. The nozzles of the diffusing rack are, for example, of the cyclone type.
Advantageously, the upper part of the degassing reactor is connected to a moisture-reducing unit.